The present invention relates to a device for directionally emitting and/or receiving electromagnetic waves, the device including at least one transmitting/receiving element, as well as a dielectric lens. The at least one transmitting/receiving element, subsequently referred to in general as aerial element, is used in this context for exciting or actually receiving the electromagnetic waves. The dielectric lens is used for generating a directional effect or desired antenna lobes. An application of the device according to the present invention is, for example, in a motor vehicle""s radar system for detecting vehicles driving in front.
A device, including at least one aerial element as well as a dielectric lens, is described, for example, in European Patent No. 0 498 524. It also describes a motor-vehicle radar system designed for detecting vehicles driving up ahead. In this case, there is a so-called bistatic radar sensor, i.e., a radar sensor having separate aerials for the transmission and receiving paths. Independently of this special feature, each of the two aerials includes a dielectric lens and at least one aerial element. The difficulty with such a device, particularly with a transmitting aerial, is that the angle of aperture of the aerial element(s) is normally wider than the dielectric lens. This means that a portion of the generated electromagnetic wave spills over the dielectric lens. Accordingly, this component is not focused by the dielectric lens in the desired direction, which reduces the overall aerial gain of the device.
PCT International Publication No. WO 97/02496 describes a monostatic radar sensor which is also designed for use in motor vehicles. In this context, monostatic means that the same aerial is used for the transmission path and the receiving path.
In this case, the aerial includes at least three aerial elements, as well as a dielectric lens positioned in front of them. To avoid lens spillover in the transmission case, it discusses positioning a so-called polyrod in front of each aerial element. This polyrod is a roughly conical dielectric body, whose dielectric properties effect a prefocusing of the generated electromagnetic wave. In this arrangement, difficulties are posed by the precise adjustment of the individual polyrods. Every deviation, be it ever so small, from the ideal position causes, in turn, lens spillover.
A device for directionally emitting and/or receiving electromagnetic waves is known from German Patent No. 197 10 811. This device is made up of at least one aerial element, a dielectric lens, and a dielectric body, which is positioned between the aerial elements and the dielectric lens. The purpose of this dielectric body is to avoid dielectric lens spillovers and to prefocus the electromagnetic waves emitted by and/or received from the aerial element. To simplify the required, exact adjustment, the dielectric body extends out two-dimensionally. The pot-shaped dielectric body forms, in conjunction with a base plate on which additional electronic components are arranged, a hermetically impervious enclosure for the aerial element and the additional electronic components.
An object of the present invention is, accordingly, to provide a device which, on the one hand, will prevent spillover of a focusing element and, on the other hand, will enable an exact adjustment of prefocusing elements.
According to the present invention, this objective is achieved by a device for directionally emitting and/or receiving electromagnetic waves, the device including at least one printed circuit board having at least one transmitting/receiving element, at least one focusing dielectric lens, and at least one additional prefocusing body, which is positioned between the transmitting/receiving element and the dielectric lens, a cover being positioned in the plane between the transmitting/receiving element and the dielectric lens, the cover having at least one bushing for the additional prefocusing body and surrounding and fixing in place the additional prefocusing body held in the bushing. An advantage of this design approach is that the cover of the present invention first of all prevents a spillover of the focusing dielectric lens, and secondly, fixes the additional prefocusing body in its position, by holding it in the bushing of the cover. This has the particular advantage of making an exact adjustment possible when mounting the prefocusing body.
It is especially advantageous that the additional prefocusing body is a dielectric rod antenna, a dielectric lens, a plane-parallel dielectric plate, an aperture plate, a slotted diaphragm, and/or a metal plate lens. All of these variants of the device according to the present invention are especially well suited for prefocusing the electromagnetic waves emitted by and/or received from the transmitting/receiving elements, in or from the direction of the dielectric lens, respectively.
In accordance with one particular embodiment of the device according to the present invention, the cover is designed to absorb electromagnetic waves. This absorption effect prevents a spillover of the focusing element in a very unique manner.
The cover rests advantageously on the printed circuit board and/or surrounds the transmitting/receiving element in a hood-like fashion. This embodiment of the device according to the present invention ensures that the transmitting/receiving elements, which are a substantial source of electromagnetic waves, are reliably covered. At the same time, the cover dimensions are no greater than necessary in this case.
In another advantageous embodiment, the cover surrounds the transmitting/receiving element right down to the location of the bushing, rendering the element impervious to high frequencies. According to the present invention, the additional prefocusing body, which focuses electromagnetic waves, but does not completely absorb or shield from them, is positioned at the location of the bushing. Because this cover is impervious to high frequencies, high frequency, electromagnetic scattered radiation is shielded in a particularly advantageous fashion and, therefore, cannot escape from the inside of the device according to the present invention.
As material for the cover, one uses advantageously at least plastic filled with graphite or plastic filled with steel fiber. These advantageous materials provide an especially good absorption and shielding effect for electromagnetic waves, depending on the ratio of graphite to plastic or steel fiber to plastic in the mixture.
In accordance with one advantageous refinement of the device of the present invention, the transmitting/receiving element is designed as a patch antenna element manufactured using microstrip technology. This type of antenna (aerial) element offers, inter alia, the advantages of large-scale production and especially small size.
The application of the device according to the present invention is especially advantageous when the occurring electromagnetic waves are in the microwave range. This is particularly the case when working with a motor vehicle""s radar system for detecting vehicles driving up ahead.
Furthermore, in accordance with a special refinement of the device of the present invention, at least one circuit arrangement is configured on the printed circuit board. This has the advantage that the component parts combined in the circuit arrangement are surrounded by the cover as well.